The invention relates generally to the field of ablation catheters, and in particular, to ultrasound-guided ablation catheters.
Physicians make use of catheters today in medical procedures that are best performed by gaining access into interior regions of the body. For example, in electrophysiological therapy, ablation is used to treat cardiac rhythm disturbances. Such a therapy may be used, for instance, to treat atrial fibrillation by forming long, thin lesions of different curvilinear shapes in heart tissue.
During these procedures, a physician steers a catheter through a main vein or artery into the interior region of the heart that is to be treated. An ablation element carried on the distal end of the catheter is positioned near the tissue that is to be ablated. For such treatments, the delivery of ablating energy must be closely governed to avoid incidence of tissue damage and coagulum formation. Further, the ablation catheters must be precisely positioned adjacent to and preferably in contact with the tissue to be treated, to insure the lesions are properly located.
Physicians and staff performing diagnostic and therapeutic procedures, such as electrophysiological therapy, typically require an imaging system to assist them in positioning the ablation catheter. Mini-transesophageal echocardiography (mini-TEE) probes are available, however, these probes must be swallowed or inserted down the patient""s throat. Such probes are poorly tolerated by patients unless they are fully anesthetized. Further, these probes can be rather large (i.e., 20 French in diameter), use complex transducer configurations and may have difficulty in detecting tissue contact by the ablation elements.
Hence, it is desirable to provide an effective apparatus which assists the physician in determining whether the ablation elements are in contact with the tissue to be ablated. It is further desirable to have such imaging systems small enough to enter narrow and tortuous regions of the patient""s vasculature. It is further desirable to have such imaging systems be located coincidental with the ablation elements to ensure tissue contact prior to ablation.
The present invention provides ultrasound-guided ablation catheters and methods for their use. Catheters and systems of the present invention will be particularly useful for precise positioning of ablation catheters prior to ablation of cardiac tissue, such as that required for the treatment of atrial fibrillation. Systems of the present invention use ultrasound transducers in the distal end of an ablation catheter to assist the operator in determining whether or not the ablation elements are in contact with the tissue to be ablated.
In one embodiment, the present invention provides a tissue ablation apparatus comprising a flexible elongate body having a proximal end and a distal end. A plurality of spaced-apart electrodes are operably attached to the flexible body near the distal end. A plurality of transducer elements are disposed between at least some of the electrodes. In this manner, transducer elements are positioned to assist the physician in detecting whether or not tissue contact is made by the proximate electrodes.
In one aspect, each electrode has at least one transducer element adjacent thereto. Preferably, the electrodes and transducer elements are operably attached to the flexible body in an alternating fashion. Still more preferably, the number of transducer elements exceeds the number of electrodes by at least one. In this manner, each electrode would have a transducer element distal thereof and another transducer element proximal thereof. By determining that the transducer elements are in contact with the tissue, the physician can presume that the intervening electrode is similarly in contact with the tissue.
In one aspect, the ablation apparatus further includes a plurality of insulators operably attached to the flexible body. The insulators operate to insulate the transducer elements from the electrodes. In one particular aspect, the flexible body has an outer diameter that is less than about eight (8) French. Ablation apparatus having such a size are sufficiently small enough to pass through the tortuous regions of a patient""s vascular system.
In one aspect of the present invention, the electrodes are spaced apart from adjacent electrodes by a gap, preferably, a gap that is between about 1.5 mm and about 3.0 mm. Preferably, at least one of the transducer elements is operably attached to the flexible body in each gap. In this manner, transducer elements and electrodes are operably attached to the body in an alternating fashion.
In one particular aspect, the transducer elements comprise cylindrical transducer elements. The cylindrical elements each have a throughhole, and the elements are positioned so that a longitudinal axis of the flexible body passes through the throughholes. In this manner, the transducer elements present a 360 degree outer surface to the surrounding tissue. Therefore, the transducer elements need not be rotated to produce an image within a 360xc2x0 image plane. In another aspect, the electrodes comprise generally cylindrical electrodes having an inner surface and an outer surface. The electrodes are positioned so that the inner surfaces face the longitudinal axis of the flexible body.
In one particular aspect, the apparatus includes between about two and about fourteen electrodes, and between about three and about fifteen transducer elements. Preferably, the electrodes and transducer elements are adapted to be connected to a controller. An ablation apparatus further preferably comprises a temperature sensing element operably attached to the flexible body. Such temperature sensing elements may be used, for example, to help monitor tissue temperatures near the ablation elements.
The invention further provides an exemplary system for ablating tissue. The system comprises an ablation apparatus ostensibly as previously described. The system includes a controller in electrical communication with the ablation elements and the transducer elements. In one aspect, the ablation elements comprise a plurality of electrodes. Alternatively, the ablation elements comprise a plurality of ablation transducer elements. In this manner, ablation may occur through the use of RF ablation or through ultrasound ablation. An exemplary description of acoustic ablation using transducer elements is described in U.S. Pat. No. 5,630,837, the complete disclosure of which is hereby incorporated by reference. It will be appreciated by those skilled in the art that other ablation elements may be used within the scope of the present invention.
Preferably, the controller comprises an ultrasound imaging and ablation controller. In this manner, ultrasound imaging is used to detect tissue contact by the ablation apparatus. The ablation of desired tissue then can occur.
In one aspect, the system further includes a plurality of leads with at least one lead operably attached to each of the ablation elements and each of the transducer elements. The plurality of leads preferably are in electrical communication with the controller to permit electrical signals to be transmitted from the controller to the ablation and transducer elements. The leads also permit signals to be sent from the transducer elements to the controller.
In a particular aspect, the system further includes a multiplexer operably attached to the flexible body, preferably near the distal end, and in electrical communication with the controller. At least some of the leads are operably attached to the multiplexer. The multiplexer operates to determine which transducer element receives electrical signals from the controller. By using a multiplexer at the distal end, the number of wires connecting the controller to the distal end may be reduced. By reducing the number of wires passing through an interior lumen of the flexible body, the outer diameter of the flexible body likewise can be reduced. Such a multiplexer will be particularly beneficial for apparatus having a relatively large number of transducer elements which together would use more wires than the multiplexer.
In one particular aspect, the transducer elements comprise cylindrical transducer elements. In this manner, the transducer elements need not be rotated to produce images within an image plane.
The invention further provides a method of ablating tissue. The method includes providing a tissue ablation apparatus as previously described with the electrodes and transducer elements being in electrical communication with a controller. The ablation apparatus is inserted into a patient and positioned proximate a tissue to be ablated. The transducer elements are energized and a plurality of reflected signals are received from the transducer elements. The method includes processing the reflected signals with the controller to determine if the transducer elements are in contact with the tissue to be ablated. If the controller determines that at least one of the transducer elements is in contact with the tissue, at least one of the electrodes is activated to ablate the tissue.
In one aspect, an ablation apparatus is provided having transducer elements and electrodes operably attached to the body in an alternating fashion. In another aspect, the reflected signals are processed to determine if one of the transducer elements is in contact with the tissue. If one of the transducer elements is in contact with the tissue, an adjacent electrode is activated to ablate the tissue.
In one aspect of the method, the reflected signals are processed to determine if all of the transducer elements are in contact with the tissue. In still another aspect, the method further includes repositioning the ablation apparatus if the controller determines that at least one of the transducer elements is not in contact with the tissue. In still another aspect, the ablation apparatus further includes a multiplexer operably attached to the body and in electrical communication with the transducer elements. The multiplexer operates to coordinate the order in which the transducers are energized.
The invention further provides a method of ablating tissue including the step of providing a tissue ablation apparatus having an elongate body, a plurality of ablation elements and a plurality of transducer elements. The ablation and transducer elements are operably attached to the body in an alternating fashion. The method includes inserting the ablation apparatus into a patient and positioning the ablation apparatus within the patient so that the ablation apparatus is proximate a tissue to be ablated. The transducer elements are energized and a plurality of reflected signals are received from the transducer elements. The method includes processing the reflected signals to determine if the transducer elements are in contact with the tissue to be ablated and activating at least one of the ablation elements to ablate the tissue if the controller determines that at least one of the transducer elements is in contact with the tissue.
In one aspect, the transducer elements are activated to ablate tissue using ultrasound energy. In another aspect of the method, the ablation elements include a plurality of electrodes for supplying current to the tissue. Alternatively, the ablation elements comprise a plurality of ablation transducers that operate to ablate the tissue using ultrasound energy.
Other features and advantages of the invention will appear from the following description in which the preferred embodiment has been set forth in detail in conjunction with the accompanying drawings.